JPS60201520A - Vertical magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled recording medium without a decrease in magnetic anisotropy in the direction vertical to the surface of a substrate even in a high- temp. atmosphere and without a decrease in coercive force in the vertical direction by forming a ferromagnetic layer, having an easy magnetization axis vertival to the surface of the substrate and consisting essentially of one kind of iron compd., on the substrate. CONSTITUTION:A ferromagnetic layer, having an easy magnetization axis vertical to the surface of a substrate and consisting essentially of iron and >=1 kind of iron compds. selected from a group of iron oxide, iron hydroxide, iron nitride, iron sulfide, and iron carbonate, is formed on the substrate. And 90-30%, by atom, iron and 10-70% element other than iron are preferably used to increase the magnetic characteristics in the vertical direction. And the magnetic characteristics in the vertical direction asre improved by the incorporation of iron oxide among other iron compds. In this case, 80-50%, by atom, iron and 20- 50% oxygen are more preferably incorporated into the ferromagnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a thin film magnetic recording medium, and particularly to a perpendicular magnetic recording medium made of iron as a raw material.

[Prior art]

As a conventional thin film perpendicular magnetic recording medium, C.

A Co-based alloy thin film represented by -Or gold alloy is used. The Co-based alloy thin film is usually formed by sputtering or electron beam evaporation.

However, when forming Co-based alloys by sputtering, the film formation rate is slow, so it is difficult to say that it is a manufacturing method suitable for mass production, and when manufacturing by electron beam evaporation using CO and Cr, the melting point of CO and Cr is low. There were problems such as difficulty in controlling the composition of the film due to large differences in saturated vapor pressure, etc. Furthermore, in any of the above manufacturing methods, in order to improve the magnetic properties in the vertical direction.

Another drawback is that the substrate must be heated to a temperature of about 150 to 300 C during film formation.

CO is used as a method to solve the above problems.

By electron beam evaporation in a vacuum atmosphere with oxygen gas introduced, vertical Co particles and non-ferromagnetic Co particles are separated.
A Co-based perpendicularly magnetized film with a mixed phase state has been proposed (Summary of the 7th Academic Conference of Japan Society of Applied Magnetics, 7aA-9
-7aA-B, November 1983).

However, Co
Perpendicular magnetic recording media using alloys based on C.

A perpendicular magnetic recording medium made of cobalt oxide and cobalt oxide has the following drawbacks because Co is used as a main component. C.

It is extremely unsuitable as a raw material for mass-produced magnetic recording media, as it is produced in small quantities, is expensive, and has large fluctuations in price, and is unstable in supply.

Furthermore, in a perpendicular magnetic recording medium composed of Co and CO oxide, when exposed to high temperatures, magnetic anisotropy occurs in the direction perpendicular to the substrate surface, and the perpendicular anisotropy magnetic field (Hk) and perpendicular coercive force decrease. There was a drawback.

On the other hand, perpendicular magnetic recording media whose main component is iron.

Its crystal magnetic anisotropy energy is smaller than cobalt. Furthermore, since it does not have a close-packed hexagonal crystal structure like cobalt, but has a body-centered cubic or face-centered cubic structure, its uniaxial magnetocrystalline anisotropy is small. Therefore, it was thought that it would be difficult to form a perpendicularly magnetized film containing iron as the main component. However, the inventors of the present invention have conducted intensive studies on the composition of the iron compound contained in the ferromagnetic layer, including the deposition conditions.

Surprisingly, they discovered that by including iron and a specific iron compound in the ferromagnetic layer, they had excellent perpendicular magnetic anisotropy, and reached a new goal.

[Purpose of the invention]

The object of the present invention is to provide a device that does not have the above-mentioned drawbacks, that is, a device that does not have a decrease in magnetic anisotropy in the direction perpendicular to the substrate surface and no decrease in coercive force in the direction perpendicular to the substrate surface even in a high-temperature atmosphere. The object of the present invention is to provide a perpendicular magnetic recording medium whose price is stable and which is suitable for mass production.

[Structure of the invention]

That is, the present invention provides a substrate having an axis of easy magnetization perpendicular to the surface of the substrate, and whose main components are iron, iron oxide, iron hydroxide, iron nitride, iron sulfide, and iron carbonate compound. This perpendicular magnetic recording medium is characterized in that a ferromagnetic layer made of at least one type of iron compound selected from the group consisting of:

Substrates that can be used in the present invention include, but are not particularly limited to, aluminum and copper.

Metals such as iron and stainless steel, and glass.

Examples include inorganic materials such as ceramics, and organic polymer materials such as plastic films. Especially IJo workability,
When moldability and flexibility are important.

Organic polymeric materials are suitable, among them polyethylene terephthalate and polyethylene naphthalate.

Polyesters such as polyethylene dicarboxylate, polyolefins such as polyethylene, polypropylene, polybutene, polymethyl methacrylate, polycarbonate, polysulfone.

Polyamide, aromatic polyamide, polyphenylene sulfide, polyphenylene oxide, polyamideimide,
Polyimide, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polytetrafluoroethylene, cellulose acetate, methyl cellulose, ethyl cellulose, epoxy [BW], urethane resins, or mixtures and copolymers thereof are suitable. Especially biaxially stretched films.

Sheets are most suitable because they have excellent flatness and dimensional stability, and among them, polyester, polyphenylene sulfide, aromatic polyamide, etc. are most suitable. The shape of the base is drum-shaped or disk-shaped.

It can be in sheet form, tape form, card form, etc.

The thickness is also not particularly limited. Sheet form.

In the case of a tape shape, card shape, etc., the thickness is preferably in the range of 2μ to 500μ, particularly 4μ to 200μ, from the viewpoint of workability and two-dimensional stability.

Prior to the formation of the magnetic recording layer described in the second section, the substrate used in the present invention is prepared to provide easy adhesion, flatness improvement9, coloration, antistatic properties,
Various surface treatments and pre-treatments may be performed for the purpose of imparting wear resistance and the like.

In the present invention, a ferromagnetic layer having an axis of easy magnetization perpendicular to the substrate surface is defined as 9th order.

The magnetic properties of the ferromagnetic layer are as follows: TIS C! It can be measured by the vibrating magnetometer method shown in -2561 or the self-recording magnetometer method. A method for measuring magnetic properties using a vibrating magnetometer method will be explained with reference to FIG. In Figure 1, O is the origin, the vertical axis shows the amount of magnetization (M) of the magnetized magnetic layer, and the horizontal axis shows the external magnetic field (H) applied to the magnetic layer.
) is shown.

When an external magnetic field (H) is applied constantly increasing in one direction to the magnetic layer of an unmagnetized measurement sample, the external magnetic field (a)
The amount of magnetization (M3) increases as indicated by the dashed arrow as It no longer increases. Point A in Figure 1 is this point. The amount of magnetization (M) at point A is called saturation magnetization (Ms). Furthermore, starting from point A, conversely, the external magnetic field (n> As the amount of magnetization (M) decreases as shown by the solid arrow, the amount of magnetization (M) also begins to decrease.

Even if the external magnetic field (H) is set to 0, the amount of magnetization (M) does not become D and remains the value of residual magnetization (Mr). In addition, the external magnetic field (
H) exceeds 0 and increases in the negative direction.

The amount of magnetization CM> becomes O. The strength of the external magnetic field (m) at this time is called coercive force (Hc). When the external magnetic field (u) is further increased in the negative direction, the amount of magnetization (M) is saturated at a certain value. This value is negative saturation magnetization (point B in Figure 1).

Furthermore, when starting from 3 points and starting to apply the external magnetic field (H) in the positive direction again, the amount of magnetization (M3 starts to increase again in the positive direction as shown by the solid arrow, and the residual magnetization point in the negative direction (-Mr)
After that, the magnetization (M) returns to the initial positive saturation magnetization point (point A in Figure 1). The curve obtained as described above is called a hysteresis loop, and this hysteresis loop causes coercive force (He) l saturation magnetization (M
Magnetic properties such as s) can be measured.

When used in a magnetic recording medium, the larger the area (S) surrounded by the hysteresis loose, the larger the recording capacity, and is suitable for high-density recording.

Sl
The area of the hysteresis loop when an external magnetic field is applied in a direction parallel to the surface of the ferromagnetic layer 9 is S7. shall be. If S, , is larger than S#, it can be said that the magnetic recording medium is suitable for perpendicular magnetic recording.

In the present invention, a ferromagnetic layer having an axis of easy magnetization in a direction perpendicular to the substrate surface is defined as a hysteresis loop area S in response to an external magnetic field perpendicular to the substrate surface, and a hysteresis loop in response to an external magnetic field in a direction parallel to the substrate surface. The magnetic anisotropy coefficient (SL/Sl) calculated from the area S is larger than 1.0, preferably 1.2 or more, and more preferably 14 or more.

In addition, the perpendicular anisotropy magnetic field (Hk) is another index that indicates the magnetic anisotropy in the perpendicular direction of a perpendicular magnetic recording medium.
It can be said that the larger this value is, the better the perpendicular magnetic recording medium can be easily magnetized in the perpendicular direction.

A method for measuring the perpendicular anisotropy field (Hk) will be explained with reference to FIG. In FIG. 2, 0 indicates the origin, the vertical axis indicates the magnetization amount (CM) of the magnetized magnetic layer, and the horizontal axis indicates the external magnetic field (H) applied to the magnetic layer. FIG. 2 shows a hysteresis loop when an external magnetic field is applied in a direction parallel to the surface of the ferromagnetic layer used as a sample. A tangent line drawn from the origin O to the hysteresis loop.

The value of the external magnetic field (H) at the intersection C with a straight line drawn parallel to the external magnetic field axis (H) passing through the positive saturation magnetization point A is the perpendicular anisotropy magnetic field (Hk).

The iron compound in the present invention is iron oxide.

These include iron nitride, iron hydroxide, iron sulfide, iron carbonate compound, etc. Specifically, the iron oxide is FeO.

Examples of iron nitrides include Fe2N, Fe4N, etc., and iron hydroxides include Fe(OH)2. Fe(OH), , Fe0OH
etc., and the iron sulfide is Fee, ・Fe253
etc., and iron carbonate compounds include FeCo, , F
e0O3・H2O, etc. Also.

Also included are non-stoichiometric iron compounds with intermediate compositions other than those described herein.

Also, the atomic cent ratio between iron and other elements is 9 for iron.
A range of 0% to 30% and 10% to 70% of other elements is desirable in order to improve magnetic properties in the perpendicular direction.

Also, among iron compounds, containing iron oxide improves magnetic properties in the vertical direction.

Containing iron oxides is highly desirable.

In this case, the atomic ratio of iron and oxygen contained in the ferromagnetic layer is preferably in the range of 90% to 30% for iron and 10% to 70% for oxygen; is 2
A range of 0% to 50% is more desirable. In addition to iron and iron compounds, the ferromagnetic layer also has properties such as corrosion resistance, wear resistance, flexibility, and surface roughness.

It is permissible to include trace amounts of other elements or compounds for the purpose of improving head touch, etc., as long as the effects of the present invention are not impaired.

The ferromagnetic layer in the present invention contains iron and an iron compound, and the thickness of the ferromagnetic layer is not particularly limited, but is practically in the range of 0.02 μm to 5 μm, and is flexible. When considering the head touch and the film formation speed of the ferromagnetic layer, the range is preferably from 0.05 μm to 2.0 μm.

Furthermore, the ferromagnetic layer in the present invention has an axis of easy magnetization in a direction perpendicular to the substrate surface, and is suitable for perpendicular magnetic recording. Even if the materials and compositions are the same, they are not included in the present invention.

Also, in the direction of adhesion between the ferromagnetic layer of the present invention and the substrate.

There is no problem in laminating one or more underlayers for the purpose of improving recording/reproducing characteristics or for other purposes.

The method for forming the perpendicular magnetic recording medium of the present invention is as follows.

Examples include, but are not limited to, reactive vapor deposition, reactive ion blating, and reactive sputtering. An example of a method for manufacturing a perpendicular magnetic recording medium using reactive vapor deposition is shown below.

The equipment used is an unwinding roll in a vacuum chamber.

A long film running system consisting of a cooling drum and a winding roller is provided, and is located directly below the cooling drum.

This is a semi-continuous electron beam evaporator equipped with an electron beam evaporator having a recessed portion. Inside the device, there is a shielding plate having an opening only in the portion directly below the drum to prevent the evaporated vapor flow having an angle between the evaporated vapor flow and the normal line of the cooling drum, that is, an incident angle exceeding 60 degrees, from entering the substrate. was placed close to the cooling dam.

An organic polymer film is placed in the running system of the device, and iron is placed in the recess of the electron beam evaporator.

At this time, the back side of the organic polymer film is cooled by a cooling drum.
It is cooled to below 0°C. First, the vacuum chamber of the electron beam evaporation apparatus is evacuated to 1 x 10-5 Torr, and then, for example, oxygen gas or nitrogen gas is applied.

An atmosphere in which a single gas or a mixture of two or more gases such as water vapor, hydrogen sulfide gas, carbon dioxide gas, etc. are introduced until the pressure within the vacuum chamber reaches 103 to 5 x 10" TOrr. The perpendicular magnetic recording medium of the present invention is formed by running an organic polymer film and evaporating iron by electron beam evaporation.

〔Effect of the invention〕

The perpendicular magnetic recording medium of the present invention has two ferromagnetic layers having easy magnetization axes in a direction perpendicular to the substrate surface, and the main components of the ferromagnetic layers are iron and iron compounds. Even when left in a high-temperature atmosphere, the magnetic anisotropy in the direction perpendicular to the substrate surface does not decrease, nor does the coercive force in the perpendicular direction. Furthermore, the raw materials used to form the ferromagnetic layer are inexpensive and there is no concern about supply, making it ideal for mass production.

Since the perpendicular magnetic recording medium of the present invention has excellent characteristics as a high-density magnetic recording medium, it can be used in perpendicular magnetic recording floppy disks, recordable/erasable digital audio disks, digital audio tapes, and perpendicular magnetic recording. Ideal for applications such as molded video tapes.

[Measurement method and evaluation criteria of characteristics]

(1) Method for measuring coercive force, saturation magnetization, and magnetic anisotropy coefficient Using a vibrating sample magnetometer (manufactured by Riken Electronics, BHV-30), apply an external magnetic field in the perpendicular and parallel directions to the substrate surface. Record the hysteresis loop for each case, and obtain the coercive force and saturation magnetization. Also.

Measure the area surrounded by the hysteresis loop with a plan meter (Kent Design Drafting Equipment ■, 906-6400), and calculate the ratio of the area of the loop in the perpendicular direction (S,) to the area of the loop in the parallel direction (S#). (S.

/S#) is the magnetic anisotropy coefficient.

(2) Method for measuring perpendicular anisotropic magnetic field Using a vibrating sample magnetometer (manufactured by Riken Denshi ■, BHV-30), a hysteresis loop is obtained when an external magnetic field is applied in a direction parallel to the substrate surface. The strength of the external magnetic field at the intersection of a tangent line drawn from the origin to this hysteresis loop and a straight line drawn parallel to the external magnetic field axis through the positive saturation magnetization point is the perpendicular anisotropy magnetic field.

(3) Method for analyzing the composition of the ferromagnetic layer The ferromagnetic layer was measured in the depth direction using X-ray photoelectron spectroscopy and Auger electron spectroscopy. ESCALAB-5 model) manufactured by the company.

Is the radiation source used for X-ray photoelectron spectroscopy Aj? - alpha rays.

The output is 10 kV - 20 mA. Etching in the depth direction is performed by Ar ion etching.

In the case of Auger electron spectroscopy, the beam voltage is 3 kV, and etching in the depth direction is performed by Ar ion etching.

Hereinafter, one embodiment of the present invention will be described based on Examples.

Examples 1 to 6 The inside of a vacuum chamber of a semi-continuous electron beam evaporation apparatus is evacuated using an exhaust system until the pressure becomes 1×11] TOrr or less.

Next, as an introduced gas, a mixed gas balanced with 20 volumes of oxygen and the balance of nitrogen was introduced through the barrier pull leak pulp until the pressure in the vacuum chamber reached 2 x 10 Torr, and a biaxially stretched polyethylene with a thickness of 50μ was introduced. The terephthalate film was run at a speed of about 2 m/min, and a film of iron and iron compounds with a thickness of 2 was formed by electron beam evaporation.
A ferromagnetic layer of 000X was continuously formed. The obtained magnetic recording medium is referred to as Example 1, and its magnetic properties are shown in Table 1. The vacuum chamber of the device is equipped with a film running system consisting of nine unwinding rolls, a cooling drum, and a take-up roll, and is equipped with an electron beam evaporator with a recess directly below the cooling drum to control the flow of evaporated vapor. A shielding plate having an opening such that the angle of incidence on the cooling drum was 16 degrees or less was placed close to the cooling drum. Further, the back surface of the polyethylene terephthalate film is cooled to 50° C. or lower. By similar devices.

A mixed gas balanced with 30 volumes of oxygen and the balance nitrogen was introduced until the pressure inside the vacuum chamber reached 1.5 x 10 Torr, and a polyethylene terephthalate film with a thickness of 50 μm was run at a speed of about 2 m/min.

A ferromagnetic layer of iron and iron compound having a thickness of approximately 2200× was formed by electron beam evaporation. This magnetic recording medium is referred to as Example 2, and its magnetic properties are shown in Table 1. In a similar device, a mixed gas balanced with 45 volumes of oxygen and the balance of nitrogen was introduced until the pressure in the vacuum chamber reached 9 x 10 Torr, and a polyethylene terephthalate film with a thickness of 25 μm was run at a speed of about 4 m/min. Then, a ferromagnetic layer composed of iron and an iron compound having a thickness of about 1 sooX was continuously formed by electron beam evaporation. This magnetic recording medium is referred to as Example 6, and its magnetic properties are shown in Table 1. The magnetic anisotropy coefficients of the magnetic recording media of the present invention in Examples 1 to B are each 1.9.
．． 1.8.2.1, all of which were 180 or more, and were perpendicular magnetic recording media having an axis of easy magnetization perpendicular to the substrate surface. Further, as a result of compositional analysis of Examples 1 to B, the main components of the ferromagnetic layer were Fe, Fe2O3, Fe,
04. It was found that it was composed of Fe(OH)2.

Further, Table 1 shows the results of measuring the perpendicular coercive force and anisotropic magnetic field after each of Examples 1 to 3 was left in a hot air oven at 160° C. for 8 hours. Example 1 as shown in Table 1
-3, there was no decrease in the perpendicular coercive force and the perpendicular anisotropy magnetic field.

Comparative Example 1 The semi-continuous electron beam evaporation apparatus shown in Example 1 was used, and a shielding plate having an opening such that the incident angle of the evaporated vapor flow to the cooling drum was 16 degrees or less was arranged inside. Polyethylene terephthalate film biaxially stretched,
Arranged with a thickness of 50μ.

With cobalt placed in the recess of the electron beam evaporator,
The vacuum chamber of the vacuum evaporation equipment was replaced with an exhaust system of 1x10 Tor.
The pressure inside the vacuum chamber is 3x10To
In an atmosphere introduced until the temperature of Formed on terephthalate film. The obtained magnetic recording medium was designated as Comparative Example 1, and its magnetic properties are shown in Table 1. Comparative Example 1 also had a magnetic anisotropy coefficient of 136, and was a perpendicular magnetic recording medium having an axis of easy magnetization perpendicular to the substrate surface. However, as shown in Table 1, the magnetic properties of Comparative Example 1 after being left in a hot air oven at 160°C for 8 hours were vertical coercive force.

The perpendicular anisotropy field decreased significantly.

Comparative Example 2 In order to perform so-called oblique evaporation inside a semi-continuous electron beam evaporation apparatus equipped with the same running system as in Example 1, a vapor flow with an incident angle of the evaporated vapor flow onto the cooling drum of 65 degrees or less was used. A shielding plate was installed to prevent the light from entering. A biaxially stretched polyethylene terephthalate film with a thickness of 50μ is placed on the winding system of this device, and electrolytic iron is placed in the recess of the electron beam evaporator, and the inside of the vacuum chamber of the electron beam evaporator is heated 5 x After exhausting the air until the temperature is below 10" Torr, only oxygen gas is released through the barrier pull leak.

The pressure in the vacuum chamber was increased to 5 x 10 Torr, and the polyester film was spread at a thickness of about 6 m/cm.
An iron-based ferromagnetic layer having a thickness of about 980× was continuously formed on the film by electron beam evaporation. The obtained magnetic recording medium was designated as Comparative Example 2, and the composition of the ferromagnetic layer of this medium was analyzed.

Fe, Fe2O3, 'Fe3O4, Fe(OH)2
It was composed of etc. However, the magnetic anisotropy coefficient of Comparative Example 2 was 0°82, and the axis of easy magnetization was not in the direction perpendicular to the substrate surface.

In addition, as shown in Table 1, the magnetic properties are low in both the perpendicular coercive force and the perpendicular anisotropy magnetic field, so that it could not be used as a perpendicular magnetic recording medium.

Comparative Example 6 Using the semi-continuous electron beam evaporation apparatus shown in Example 1, biaxial stretching was carried out in the running system of the apparatus without disposing a shielding plate to limit the incident angle of the evaporated vapor flow inside. A polyethylene terephthalate film with a thickness of 50 μm was placed, and iron was placed in the recess of the electron beam evaporator, and the vacuum chamber of the vacuum evaporator was evacuated to a temperature of 1 x 10 Torr or less.
running the polyethylene terephthalate film at a speed of about 8 m/min without introducing gas;
An 800× thick iron film was continuously formed by electron beam evaporation. The obtained magnetic recording medium was designated as Comparative Example 6.

The magnetic properties are shown in Table 1. The magnetic anisotropy coefficient of Comparative Example 6 was 0.08, which still had a perpendicular coercive force.

Both the perpendicular anisotropic magnetic fields are small values as shown in Table 1.
Comparative Example 3 could not be used as a perpendicular magnetic recording medium.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a hysteresis loop used to measure magnetic properties, and FIG. 2 is a schematic diagram of a hysteresis loop used to measure a perpendicular anisotropic magnetic field. 0: Origin Point M: Amount of magnetization H: External magnetic field A: Positive saturation magnetization point B: Negative saturation magnetization point C: Intersection point Hk: Vertical anisotropic magnetic field Patent applicant Azuma Shi Co., Ltd. Second Bacteria Showa Date: Manabu Shiga, Commissioner of the Japan Patent Office 1, Indication of the case, Patent Application No. 55170 of 1982, 2, Name of invention: Perpendicular magnetic recording medium 46, Date of amendment order: Voluntary action 5, Number of inventions increased by amendment: None 6, Column 7 of “Detailed Description of the Invention” in the specification subject to amendment, content of amendment (1) r300cJ in line 8 of page 2 of the specification is changed to “300°C
” he corrected. (2) "35" on page 12, line 7 of the same book is corrected to "45". (3) “J becomes less than or equal to U” in line 14 of the same page of the same book.
and correct it. (4) r103J on the 18th line of the same page in the same book as “2×10-3
” he corrected.

Claims (1)

[Claims] (1) On the substrate, the axis of easy magnetization is perpendicular to the substrate surface, and the main components are iron, iron oxide, iron hydroxide, iron nitride, iron sulfide, and iron carbonate compounds. A perpendicular magnetic recording medium characterized in that a ferromagnetic layer made of at least one selected iron compound is formed.